The present invention relates to an electrotherapy apparatus comprising a sensor for detecting periodically recurring signal peaks, in particular the R-R peaks of an electrocardiogram of a person, a processor for deriving from the periodically recurring signal peaks a time delay corresponding to approximately the end of the T-wave, and a trigger system or circuit initiated by an output signal of the processor or embodied within the processor for applying electrical stimulations to one or more active electrodes provided on the person at a time related to the end of the time delay. Furthermore the invention relates to methods of using such electrotherapy apparatus.
Electrotherapy apparatus of the initially named kind is described in the international patent application with the publication number WO 01/13990 A1, now expired.
The electrotherapy apparatus described there is adapted to stimulate the muscles of the body of a person or a mammal using so-called counter-pulsation. That is to say, the momentary heart beat of the person or mammal is determined generally by detecting the R peaks of an electrocardiogram derived in real time from the person or mammal being treated. From the distance in time measured between the last two R peaks a time is calculated corresponding to the end of the T-wave of the electrocardiogram using the known so-called Bazett relationship. The electro-stimulation pulses are then applied to the selected muscle generally starting within a window which extends from 5% of the length of the R-R path before the end of the T-wave to a position up to 45% of the length of the R-R path after the end of the T-wave.
It has been found that this type of electrotherapy leads to extremely beneficial effects with respect to the heart of the person or mammal and, depending on precisely how the electrotherapy is carried out, can also be used for curing a whole spectrum of adverse conditions.
In the aforementioned document WO 01/13990 the beneficial effect is primarily attributed to the specific shape of the curve in FIG. 3 of that reference showing a hump in the blood pressure curve just after the onset of diastole which considerably increases the flow through the coronary arteries of the patient concerned, thus leading to an improvement of the condition of the heart muscles.
The experiments conducted to date seem to suggest that this explanation is only part of the story and that in fact even quite small local stimulations of a person or patient can lead to increased perfusion in the small peripheral blood vessels resulting in a significantly lower back pressure on the heart which itself improves the working of the heart. It is believed that some form of bio-feedback is taking place via the autonomous nervous system and that this accounts for the astonishing results that have been achieved.
The aforementioned document WO 01/13990 describes that, although the treatment can be carried out using just one neutral electrode and one active electrode, it is better if a plurality of active electrodes are used. The reason is that the human body becomes accustomed to the applied pulses and, if only one active electrode is provided, then the muscles affected by the electro-stimulation signals gradually become tired and are stimulated less effectively. By applying the stimulating pulses to different active electrodes in sequence it is possible to ensure that the muscle groups affected by the applied impulses do not become tired. It is stated that the minimum number of active electrodes for sequencing is two and a specific embodiment is described in which the train of stimulating pulses is applied in sequence to first, second, third and fourth electrodes.
The apparatus described in WO 01/13990 is provided with a safety cut-out function, meaning that the apparatus switches off automatically if the patient's heart rate goes too high or too low, or if a patient's blood pressure becomes too high or too low or when arrhythmia is detected.
The prior art reference also describes a problem called interference.
This problem can be described as follows. When using any measured heart QRS trace (an electrocardiogram), a trigger signal for detecting the patient's heart rate is usually derived from the positive rising slope of every R peak. The trigger signal is generally a digital trigger signal and initiates the electrical muscle simulation signal after the required delay at a time within the time delay window described earlier. Since this stimulation signal is an electrical signal with a magnitude many times higher than the heart rate signal itself, the electrical stimulation impulse is transmitted on the human body and consequently the heart signal sensor also senses the electrical stimulation signal. If now the control setting of the electrotherapy apparatus is such that a stimulation pulse for the muscle is delivered in counter-pulsation to the heart (i.e. at the end of the T-wave), the trigger unit first receives from the heart rate sensor the wanted trigger input representing an R peak. Moreover, during the R-R cycle, exactly at the moment of the muscle stimulation, a much higher electrical stimulation signal is delivered to the muscle which is interpreted as another R peak and results in a further trigger signal. This trigger signal then leads to a second unwanted muscle stimulation within the same R-R cycle at exactly the same delay but now after the further trigger signal. This second unwanted stimulation is perceived by the stimulated person as a sudden surprising disturbance which is completely irregular in comparison to the calming rhythm expected from the counter-pulsation mode. As a result the heart rate immediately increases sharply, probably via neuro-transmission to the brain and back to the heart. Synchronized stimulation counter-pulsation does not work when such interference is present and the wanted heart load reduction cannot then be achieved.
In order to overcome this problem the reference WO 01/13990 provides a gating mechanism which effectively closes an interference window after a trigger signal from a heart rate sensor has been registered by the electrotherapy apparatus. This interference window is reopened by the electrotherapy apparatus in time to accept the wanted trigger pulses but to avoid unwanted trigger pulses resulting from electro-stimulation.
The WO reference describes one practical execution of the gating mechanism defining the interference window. This gating mechanism is realized in the form of software controlling a microprocessor whereby the rising edge of the digital trigger signal triggers the microprocessor into an interrupt routine and then the closing of the interference window is activated by a software gate which disables the acceptance of any unwanted trigger signal. Thus a further trigger signal resulting from electro-stimulation is prevented from being transmitted to the microprocessor as long as the interference window is closed. Closing and opening of the interference window is set by programmable adjustable setting values which are selected relative to the measured R-R cycle.
The WO reference also describes a practical programmable algorithm which defines the way an adaptive control unit in the electrotherapy apparatus can automatically find the lowest possible heart load. In accordance with the description given in the WO reference, first of all realistic minimum and maximum values for the delay are defined, i.e. for the delay from each R peak to the triggering of a stimulation signal. These limits are set relative to the prevailing heart rate as measured from successive R-R peaks. The minimum delay will usually be selected at or just before the start of the delay window, i.e. at or just before a time corresponding to 5% of the R-R path before the expected end of the T-wave, for example as calculated using the so-called Bazett relationship. As a safety precaution a maximum delay can also be selected which should not be later than 45% of the length of the R-R path after the end of the T-wave. The maximum delay could, however, be omitted.
An offset value is now defined and is added to the minimum delay and used to define the time at which stimulation signals start. A typical initial value for the offset could be 5% to 10% of the R-R paths. Stimulation is now commenced using this time delay; i.e. minimum delay plus offset and the heart rate are monitored by measuring the distance between successive R-R peaks. If a reduction of the heart rate, i.e. a lengthening of the R-R path, occurs, then a reduction in the offset is effected by a predetermined amount, for example a fixed fraction of the original offset, and a check is again made as to whether the heart rate has reduced. If so the offset is again reduced and this process is continued until no further reduction in the heart rate is detected, or alternatively, until the minimum heart rate set in the safety cut-out has been reached or until the heart rate increases again.
A renewed increase in the heart rate indicates that the delay (minimum delay plus offset) is no longer at an optimum value.
If the heart rate increases then the offset should also be increased in an attempt to reduce the heart rate. Once the heart rate starts to increase again then this is an indication that the offset is now too large. This signifies that the optimum value of the offset has been found, namely the value of the offset which resulted in a minimum heart rate. The offset can now be returned to this optimum value. Once a suitable offset value has been determined it can be retained for future use.
Although the WO reference provides a practical system for determining the required offset or the total time delay from each R peak to the triggering of a stimulating electrical pulse, and also practical realizations of the electrotherapy apparatus, there is scope for improvement, particularly with patients suffering from arrhythmia. In patients with such arrhythmia, an irregular heart beat, this means that reliance on a previously measured distance between two R-R pulses in order to determine the time at which a stimulating electrical signal should next be triggered can lead to triggering at undesired times and to discomfort for the patient.
Moreover, although the existing apparatus as described in the WO reference can be used in many applications with beneficial effect there is a desire to increase the performance of the electrotherapy apparatus and to increase its scope of use.